Security researchers have uncovered a recent distributed denial-of-service (DDoS) attack that used at least 162,000 WordPress-powered websites to knock another site offline.

The technique made it possible for an attacker with modest resources to greatly amplify the bandwidth at its disposal. By sending spoofed Web requests in a way that made them appear to come from the target site, the attacker was able to trick the WordPress servers into bombarding the target with more traffic than it could handle. Besides causing such a large number of unsuspecting sites to attack another one, the attack is notable for targeting XML-RPC, a protocol the sites running WordPress and other Web applications use to provide services such as pingbacks, trackbacks, and remote access to some users.

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You don't need to be a genius to debug a pf.conf firewall ruleset, you just need the guts to run tcpdump